Active Respiration of Fish in Relation to Ambient Concentrations of Oxygen and Carbon Dioxide

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Abstract
The oxygen consumption at a steady rate of activity maintained by a mild electric stimulus was measured for Salvelinus fontinalis (Mitchill), Catostomus commersoni (Lacepede), Ameiurus nebulosus LeSueur, Cyprinus carpio (Linnaeus) and Carassius auratus (Linnaeus) in the presence of various combinations of oxygen and carbon dioxide. At a given level of oxygen the logarithm of the rate of oxygen consumption decreases linearly with the concentration of carbon dioxide. The linear relation so found is characteristic of a given species and the sensitivity to carbon dioxide decreases with increasing acclimation temperature. The oxygen concentration determines the level of active oxygen consumption in the absence of carbon dioxide and when the concentration approaches the lower lethal limit the effect of the addition of carbon dioxide is enhanced. The data found for these species for active metabolism was combined with data in the literature for resting metabolism to give estimates of the metabolism available for activity. The respiratory sensitivities of the four species were further compared by considering the estimated combinations of oxygen and carbon dioxide required to bring about asphyxiation in both flowing water and sealed containers. The ability of the blood of the fish to take up oxygen in the presence of carbon dioxide shows no direct relation to the ability of the fish to transport oxygen to the external medium under similar circumstances.